1. Field of the Invention
This invention relates to enzyme compositions and methods of using these enzyme compositions, inter alia, to degrade succinoglycan.
2. Description of the Related Art
Succinoglycan is a heteropolysaccharide polymer composed of many monosaccharide units linked by glycosidic bonds produced as high molecular weight polymers and low molecular weight oligosaccharides by a variety of bacteria genera. Succinoglycan generally comprises glucose, galactose, pyruvate, succinate, and acetate. The exact composition of succinoglycan, however, depends on the microorganism producing it as well as the microorganism cultivation conditions. Generally, succinoglycan is composed of repeating units comprising about one galactose and about seven glucose molecules joined by beta-1,4-, beta-1,3- and beta-1,6-glycosidic linkages and is adorned by acetate, pyruvate and succinyl groups. More specifically, succinoglycan may comprise glucose and, for each about 7 moles of glucose, about 0.9 to about 1.2 moles of galactose and about 0.65 to about 1.1 moles of pyruvate, together with succinate and acetate in molar proportions (for each about 7 moles of glucose) between about 0 and about 2.
Succinoglycan is often used in various industries, inter alia, for viscosifying aqueous fluids. For example, in the personal care product industry succinoglycan may be used to viscosity such products as shampoos and the like. In the upstream energy industry, operations in well bores penetrating subterranean formations often involve the use of viscosified treatment fluids that may comprise succinoglycan. Viscosified treatment fluids may be added to a well bore to facilitate the completion of a specific operation on all or a portion of the well bore, e.g., drilling, fracturing, gravel-packing, and the like. Other commonly used viscosifying additives include various polysaccharides such as xanthan, guar, hydroxyethylcellulose, and the like.
In some applications, after a viscosified treatment fluid has performed its desired function, the fluid may be “broken,” meaning that its viscosity is reduced. In certain subterranean applications, breaking the fluid is beneficial to the production process because, inter alia, it likely will speed separation of particulates such as proppant or gravel from the viscosified treatment fluid. Breaking a viscosified treatment fluids is usually accomplished by incorporating “breakers” into the fluids. Traditional breakers include acids, oxidizers, enzymes, and the like. Although useful for reducing the viscosity of a viscosified treatment fluid, breakers oftentimes are not specific to the treatment fluid and may degrade a filter cake formed by a treatment fluid, especially if the filter cake comprises components susceptible to the breaker.
Generally, in a drilling operation, filter cakes will form on the walls of the well bore as a deposition of various residues from subterranean operations such as drilling, fracturing, gravel packing, and the like. Such filter cakes are often tough, dense, substantially water insoluble, and capable of reducing the permeability of the surface on which they have formed. Filter cakes often comprise precipitates such as silicates or calcium compounds. Filter cakes also may comprise compounds referred to above as viscosifying additives, e.g., xanthan, succinoglycan, or another polysaccharide. Although some fluids used in well bore operations do not form filter cakes, these fluids may create conditions analogous to those found within filter cakes. Therefore, the term “filter cake” when used herein also refers to these conditions.
Filter cakes are desirable, at least temporarily, in subterranean operations for several reasons. For one, a filter cake may act, inter alia, to localize the flow of a treatment fluid and minimize fluid loss problems. This is an important function of a filter cake because, inter alia, if too much fluid is lost, the conductivity or permeability of the formation may be damaged. A filter cake may also add strength and stability to the formation surfaces on which the filter cake forms. The filter cake may be beneficial to other well bore operations, for example, hydraulic fracturing and gravel packing. Although desirable for a certain amount of time or application, in order to produce the desirable fluids from the formation, the filter cake generally is removed thereafter. Accordingly, the treatment fluids also, generally comprise an additional component that is capable of degrading the non-succinoglycan components of the filter cake such as acids, oxidizers, or enzymes.
In some instances, it is necessary to break a viscosified treatment fluid without negatively impacting the filter cake and vice versa. In other instances, it would be desirable to be able to break both the viscosified fluid and the filter cake with the same breaker.